The Magpies' followers expressed their discontent at St Mary's following Newcastle's 4-0 defeat on Saturday.
"I understand the fans' reaction at the end," Santon told the club's official website. "I went over to say thank you, as I always do, and they booed, but I understand because they deserve more from us, and they are right.
"We looked like we played with no passion and we just want the season to finish. That isn't true, but we were not good enough.
"It could have been 8-0 or 9-0, and it doesn't have to be like this."
Newcastle are currently ninth in the Premier League table.